This is because when a massive planet orbits a star, the wobble produced in the star increases with a larger separation between the planet and the star, and at a given distance from the star, the more massive the planet, the larger the wobble produced. This technique, called the astrometric technique, is expected to be particularly good for detecting Jupiter-like planets in orbits distant from the star. The planet is revealed indirectly if that location, called the barycenter, is far enough from the star's center to cause a wobble detectable by a telescope. The star and the planet orbit a location that represents the center of mass for both combined. It involves tracking the star's actual motion in space, then detecting a minuscule "wobble" in that motion caused by the gravitational effect of the planet. The technique has long been known, but has proven difficult to use. This is the first discovery of an extrasolar planet with a radio telescope using a technique that requires extremely precise measurements of a star's position in the sky, and only the second planet discovery for that technique and for radio telescopes. Using the supersharp radio "vision" of the continent-wide Very Long Baseline Array (VLBA), astronomers have discovered a Saturn-sized planet closely orbiting a small, cool star 35 light-years from Earth. The results are published in the current issue of the “Astronomical Journal“. Other planet search techniques have difficulties to study these dwarfs, mainly due to the faintness of the objects, which makes radio observations a very powerful and complementary tool to uncover many more new planets. Only a handful of extrasolar planets with characteristics similar to TVLM 513 b have been discovered so far around small, cool stars – known as ultracool dwarfs. One of the things that makes this detection exciting is that the planet, called TVLM 513 b, has a similar mass to Saturn and an orbit analogous to that of Mercury in our Solar System. The discovery was possible thanks to the extremely high precision measurements of the star’s position that can only be achieved with such a radio telescope network. For their observations, the researchers used a network of radio antennas that are linked together to form a continent-size radio telescope. This is the first time that this technique is successfully employed with observations obtained at radio wavelengths. An international team of astronomers including Gisela Ortiz-Leon from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn discovered a Saturn-like planet orbiting a small, cool starby detecting the "wobble" in the star’s motion caused by the gravitational pull of the planet.
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